Re: [RFC PATCH v2 09/30] target/loongarch: Add TLB instruction support

[Richard Henderson]

On 11/17/21 8:29 AM, yangxiaojuan wrote:
> On 11/12/2021 02:14 AM, Richard Henderson wrote:
> > On 11/11/21 2:35 AM, Xiaojuan Yang wrote:
> > > +static bool trans_tlbwr(DisasContext *ctx, arg_tlbwr *a)
> > > +{
> > > +    gen_helper_check_plv(cpu_env);
> > > +    gen_helper_tlbwr(cpu_env);
> > > +    tcg_gen_movi_tl(cpu_pc, ctx->base.pc_next + 4);
> > > +    ctx->base.is_jmp = DISAS_EXIT;
> > > +    return true;
> > > +}
> >
> > I think you can skip the EXIT if paging is disabled, which it usually will be 
> > in the software tlb handler.  You'd be able to tell with the mmu_idx being the 
> > one you use for paging disabled.
>
> The paging disabled only enabled at the bios startup, we can get the phys 
> address directly, tlbwr instruction will not be used when paging enabled.

Paging is also disabled during TLBRENTRY exception (see section 6.2.4 Hardware Exception 
Handling of TLB Refil Exception).  It is this routine that will usually use tlbwr most 
often (although the kernel at PRV 0 is not prevented from doing so).

> > > +    default:
> > > +        do_raise_exception(env, EXCP_INE, GETPC());
> >
> > You can detect this during translation, and dispatch to the appropriate invtlb 
> > sub-function.
> oh, sorry, I don't quiet understand this. detect during the translation sees 
> more complicated.

It is not more complex at all.  Less complex, I would say.

static bool trans_invtlb(DisasContext *ctx, arg_invtlb *a)
{
    TCGv rj = gpr_src(ctx, a->rj, EXT_NONE);
    TCGv rk = gpr_src(ctx, a->rk, EXT_NONE);

    if (check_plv(ctx)) {
        return false;
    }

    switch (a->invop) {
    case 0:
    case 1:
        gen_helper_invtlb_all(cpu_env);
        break;
    case 2:
        gen_helper_invtlb_all_g(cpu_env, tcg_constant_i32(1));
        break;
    case 3:
        gen_helper_invtlb_all_g(cpu_env, tcg_constant_i32(0));
        break;
    case 4:
        gen_helper_invtlb_all_asid(cpu_env, rj);
        break;
    case 5:
        gen_helper_invtlb_page_asid(cpu_env, rj, rk);
        break;
    case 6:
        gen_helper_invtlb_page_asid_or_g(cpu_env, rj, rk);
        break;
    default:
        return false;
    }
    ctx->base.is_jmp = DISAS_STOP;
    return true;
}


r~